Improve bash lexer to support math:
Improve bash lexer to support math:

{{{
echo $(( 1 + 2 ))
}}}

erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments,erickt/pygments